Boom stop apparatus



March 1964 D. c. MARKWARDT ETAL 3,123,223

BOOM s'roP APPARATUS 3 Sheets-Sheet 1 Filed Aug. 13, 1962 INVENTORS ATTORNEY March 3, 1964 D. c. MARKWARDT ETAL 3,123,223

BOOM STOP APPARATUS 3 Sheets-Sheet 2 Filed Aug. 13, 1962 ATTORNEY i1 R T 8 4% O DONALD C. MARKWARDT 8| ROCHE J- VAN DE HEY mmc D. c. MARKWARDT ETAL 3,

BOOM STOP APPARATUS 3 Sheets-Sheet 3 R Y m m m v a W m T H A m H m M M W E m w M 0 O R D 7 m Q U 3 w wm I! u m :1 Ex

$Q\ 1| 3 1 L H Lv. l .WWII nllfl" w lllllllll 1| March 3, 1964 Filed Aug. 13, 1962 United States Patent 3,123,223 BQQM STOP APPARATUS Donald C. Markwardt, Manitowoc, and Roche J. Van De Hey, Whitelaw, Wis., assignors to The Manitowoc (30., Inc., Manitowoc, Wis., a corporation of Wisconsin Filed Aug. 13, 1962, Ser. No. 216,404 12 Claims. (Cl. 212-59) This invention relates to load-handling equipment having elongate boom structure pivotally mounted to base support structure, and more particularly to boom stop apparatus for cushioning, limiting, hindering, stopping, arresting, restraining or in other ways preventing the boom structure from suddenly recoiling toward or moving backward over the base support structure of the load-handling equipment.

In load-handling equipment, such as crane assemblies or other like machines, there is usually provided elongate boom structure which is pivotally mounted adjacent one end portion thereof to an upper works or base support structure for movement in a generally vertical plane, be tween lowered and raised positions, by a which supported on the upper works of the crane assembly or the base support structure of the machine through a boom cable arrangement attached adjacent the other end portion or the boom point of the boom structure.

A load is normally attached to a load cable arrangement which is carried by a boom point sheave at the boom point of the boom structure and extends to a winch which may also be supported on the upper works of the crane assembly or the base support structure of the machine.

In most loadhandling equipment of this type, the boom structure is mounted to be raised to a generally vertical position, i.e., a position more vertical than horizontal, in substantially overlying relationship to the upper works of the crane assembly or the base support structure of the machine. At certain times, it is necessary to operate the equipment with the boom structure in a nearly vertically disposed position. The weight of the boom structure, when so disposed, places the boom cable arrangement in tension which is greatly increased when the load cable arrangement engages a load. If the load cable arrangement should fail, release, break or otherwise become suddenly disengaged from the load, the tension of the boom cable arrangement is also suddenly released causing the boom structure to recoil or move toward the upper works or the base support structure, as the case may be. This recoil or movement often causes the boom structure to swing beyond the vertical and back upon the upper works of the crane assembly or the base support structure of the machine to damage same and possibly injure the operator thereof.

A similar problem is encountered and occurs when using similar equipment having an attachment such as a ball for demolition work, should the ball swing backwardly beyond the vertical pivot mounting of the boom structure to the upper works or the base support structure during the operation thereof.

Numerous types of means are known for arresting this type of boom structure recoil or movement before damage to the equipment or operator ensues. Some of the known means have proven unduly complicated and therefore have presented maintenance problems. Others could be connected only when the boom structure was raised to a particular height with the consequent expenditure of much time and effort. Telescoping type boom structure stop means have been used but inasmuch as it is necessary to attach such boom stop means to the boom structure and to the upper works of the crane assembly or base support structure of the machine, a considerable distance from the pivotal mounting of the boom structure thereto, an excessive long length assembly is necessary if the boom ice structure is to be lowered to ground level. Boom stop means are also known that utilize hydraulic means to arrest the recoil or movement of the upper works of the equipment but such hydraulic means are usually somewhat diflicult to maintain since there is generally a leakage of the fluid which is employed with such hydraulic means.

It is therefore an object of this invention to provide boom stop apparatus that will permit pivotally mounted elongate boom structure to be lowered to substantially ground level without requiring the disconnection of the boom stop apparatus therefrom.

A further object of this invention is to provide boom stop apparatus that utilizes a source of air under pressure to cushion, limit, hinder, stop, arrest, restrain or otherwise prevent a sudden recoil action or backward movement of pivotally mounted elongate boom structure.

A still further object of this invention is to provide improved boom stop apparatus having a linkage device which is interconnected between base support structure and elongate boom structure which is pivotally mounted to the base support structure.

It is also a further object of the invention to provide boom stop apparatus with a linkage device having a plurality of members wherein one of the members of such device is extensible and retractable together with a retarding feature which retards the retraction of the one member until after another member of the linkage device has been pivoted into bearing engagement with base support structure to which a boom structure may be pivotally mounted.

7 Another object of this invention is to provide boom stop apparatus having a linkage device with an adjustable feature for enabling the apparatus to be adjustable to compensate for wear and the operational eliect of the apparatus.

It is also another object of this invention to provide boom stop apparatus comprising a linkage device having a longitudinally extensible and retractable elongate member carrying a source of air under pressure with a stopguide and abutment feature which on retraction of the elongate member is operable to further compress the air.

In order to accomplish the objects and overcome the undesired features of known boom stop means, as stated above, the boom stop apparatus of this invention comprises a linkage device which includes a pair of elongate pivotally interconnected members one of which is longitudinally retractable and extensible and which is further pivotally connected to an intermediate portion of an elongate boom structure which is in turn pivotally supported by a base support structure, such as an upper works of a crane assembly, to which another member of the linkage device is pivotally connected so that the linkage device is disposed between and pivotally connected to the elongate boom structure and the base support structure. The extensible and retractable member of the linkage device is provided with a source of air under pressure which is confined within a cylinder having a piston from which there extends a piston rod and suitable guide-stop-albutment arrangement is provided for enabling a part of the extensible and retractable member to engage the piston rod and further compress the air in the cylinder when the member of the linkage device is retracted on movement of the boom structure toward the vertical. The extensible and retractable member of the linkage device is also provided with retarding structure for retarding the retraction thereof until after the member of the linkage arrangement which is pivotally mounted to the base support structure is moved to a position wherein the member is in engagement with and supported by an inclined part of the base support structure so that this member is disposed in such engagement with the base support structure prior to the retraction of the other member of the linkage device. Suitable adjustments are provided for enabling the linkage device to be adjustable to vary the effect thereof and also to compensate for any wear in the various elementswhich are associated in interconnected relationship therewith and such adjustments relate to the pivotal location of the member to the base support structure as well as the effective engagement of the abutment of the guidestop arrangement which engages the piston rod of the source of air under pressure.

Other objects and important features of the invention will be apparent from a study of the specification following taken with the drawing, which together show, illustrate, describe and disclose a preferred embodiment and modification of the invention and what is now considered to be the best mode of practicing the principles thereof. Other embodiments and modifications may be suggested to those having the benefit of the teachings herein and such other embodiments or modifications are intended to be reserved especially as they fall within the scope and spirit of the subjoined claims.

In the drawing:

FIGURE 1 is a side elevational view of load-handling equipment, illustrated in the form of a mobile type crane assembly with parts thereof being broken away to better illustrate same, and showing boom stop apparatus of this invention incorporated therewith with such boom stop apparatus being illustrated in solid lines as disposed in a first position wherein the boom structure or" the equipment is lowered or substantially horizontal and in dotted lines when the boom structure is nearly vertical or raised;

FIGURE 2 is an enlarged more detailed showing of the boom stop apparatus, as illustrated in FIGURE 1, showing the boom stop apparatus in similar positions as illustrated therein;

FlGURE 3 is a detailed enlarged partial view of a part of one of the elongate members of a linkage device of the boom stop apparatus;

FIGURE 4 is an enlarged plan view of another part i of the elongate member as illustrated in FIG. 3 and showing more detail than as shown in FIGURES 1 and 2 of the drawing;

FIGURE 5 is a side elevational view of the part of the member which is illustrated in FIGURE 4 of the drawing, and

FIGURE 6 is a detailed illustration of a connection between certain parts of thesboom stop apparatus.

Attention is now directed to FIGURE 1 of the drawing wherein there is illustrated load-handling equipment, preferably in the form of a crane assembly do or other like machine, having elongate boom structure 12, pivotally mounted through pivot 14 adjacent one end portion 16 thereof, to base support structure which, as illustrated, may be an upper works 18 of the crane assembly ltl.

In accordance with conventional practice, a boom cable arrangement 26 is provided for holding, mounting and positioning the boom structure 12. by raising and lowering same through a generally vertically disposed plane, and a load handling arrangement 22 is also provided for engaging, attaching or otherwise securing a load in a manner which will enable the boom structure 12 to handle same, as desired.

Disposed intermediate the boom structure 12 and the base support structure or the upper works 18 there is provided boom stop apparatus 24 for cushioning, limiting, bulfing, hindering, stopping, arresting, restraining or in other ways preventing the boom structure 12. from suddenly recoiling toward or moving backward over the base support structure or upper works 18 of the equipment It as a result of failure, release, breaking or other sudden disengagement of a load being handled by the equipment through the employment of the load handling arrangement 2 2.

The boom stop apparatus 24 preferably comprises a pair of linkage devices 26 pivotally interconnected to and extending between opposed side portions of the boom structure 12 and the base support structure or upper works 13 of the equipment lit with the linkage devices 26 being disposed in substantially parallel relationship relative to each other and each provided with an elongate bodily extensible and retractable first link-like member 28 pivotally mounted adjacent one end portion 3%) thereof to an intermediate portion 32 of the boom structure 12 and a second elongate bodily rigid link-like member 34 having a fixed length and pivotally connected adjacent one end portion so thereof to the base support structure or the upper works iii of the machine ill with the other end portions of the members 26 and 34 being pivotally connected together, as will be described and disclosed in more detail hereinafter.

In actual practice, while the boom stop apparatus 24 preferably comprises at least one pair of the linkage devices 2%, for the sake of brevity, only one of the linkage devices shall now be described and disclosed.

As shown in more detail in FIGURE 2 of the drawing, each of the linkage devices 26 of the boom stop apparatus 24 has the respective bodily extendible and retractable first link-like member 28 thereof defined by an elongate tube or sleeve-like part 38 which has the one end portion 39 pivotally mounted by a suitable pivotal connection to the intermediate portion 32 of the boom structure 12 with the other end portion thereof being telescopically received within an open end portion 42 of an elongate tubular or sleeve-like part 44 with the other end portion of the part 44 supporting a container or cylinder of air 46 under pressure.

The bodily rigid non-extendible and non-retractable second link-like member 34 of each of the linkage devices 26 is defined by an elongate strut-like part 48 which has the one end portion 36 thereof pivotally mounted tothe base support structure or upper works 18 of the equipment 1% through an A-frame support structure so from which the strut-like part 5$ projects with the other end portion thereof being pivotally connected by pivot 52 to the other end portion of the sleeve-like part 44. A guide 54 having an arcuate configuration is carried by the A-frame support structure 50 for guiding the strut-like part 48 during the pivotal movement thereof.

As shown in FIGURE 3 of the drawing, there is shown a guide-stop-abutment arrangement wherein the other end portion 4t? of the sleeve-like part 38 is provided with an abutment 56 having an opening 53 through which extends an end portion of an elongate bodily rigid stop-guide rodlike part 66 which is maintained therein by a suitable removable and adjustable enlarged end portion 62 which may be in the form of a nut threaded thereon.

On movement of the boom structure 12 from a generally horizontal position, i.e., more horizontal than vertical, as shown by solid lines in FIGURES 1 and 2 of the drawing, the part 33 telescopes into the part 44 to retract or decrease the length of the first link-like member 28 with the stop-guide rod-like part on acting in a manner to guide and maintain the parts 38 and 44 in operative assembled relationship with the enlarged end portion 62 of the stop-guide rod-like part 6t) being received within the confines of the part 54. A reverse movement of the boom structure 12, i.e., from a vertical to a substantially horizontal position, will result in the extension of the link-like member 23, with the part 38 prevented from extending beyond a desired length by the engagement of the enlarged end portion 62 of the stop-guide rod-like part 60 and the abutment S6 of the arrangement which is on the other end portion ill of the sleeve-like part 38.

Positioned within the confines of the container or cylinder 46 is a piston 64 having a rod 636 which extends therefrom and terminates within the confines of the sleevelike part 44 of the member 28 whereat the piston rod 66 is secured to the other end portion 68 of the stop-guide rod-like part as by a clevis type connection 70. On retraction or contraction of the link-like member 28, as described above, the abutment 56 on the other end portion 40 of the sleeve-like part 38 will engage the clevis type connection 70 and urge the piston 66 into a compression stroke to further compress the air which is confined within the container or cylinder 46.

If desired, an adjustment 72 may be provided for effectively varying the engagement of the abutment 56 of the arrangement 60 and the clevis type connection 70 of the piston rod 66 on retraction or contraction of the linklike member 28. As illustrated in FIGURES 2 and 6 of the drawing, the adjustment 72 is provided along the piston rod 66 and it is to be understood that the adjustment 72 may also be placed along the stop guide rod-like part 60, if preferred.

In passing and as shown in more detail in FIGURES 4 and of the drawing, the other end portion of the sleeve-like part 44 is provided with a pair of longitudinally extending laterally spaced, substantially parallel plate-like elements 74 which are interconnected by laterally extending supports 76 to which there is secured, by suitable structure such as welding or the like, the container or cylinder 46. The adjacent end portions of the platelike elements 74 are each provided with a bore 78 and the container or cylinder 46 is provided with a bifurcated end portion 80 presenting laterally aligned openings 81 therein which are aligned with the bores 78.

The container or cylinder 46, as shown in FIGURES 2 and 4 of the drawing, is provided with an intake port 82 which is in communication with a source of air under pressure through conduit structure 84 and an exhaust port 86 open to atmosphere. The conduit structure 84 of each system is provided with one-way check valving 88 and, as illustrated in FIGURE 2 of the drawing, the systems pass through an arrangement in a king pin mechanism 90 of the upper works 18 of the crane assembly and may be connected to the source of air pressure used for braking the crane assembly 10* or some other suitable source, as desired or required.

The other end portion of the strut-like part 48 of the second link-like member 34 is pivotally connected to the plate-like elements 74 of the sleeve-like part 44 and the bifurcated end portions 80 of the container or cylinder 46 by the pivotal connection 52 which employs a pin that passes through the aligned bores 78 and openings 81 which are respectively formed therein. Also, as shown in FIG- URE 2 of the drawing, adjacent the other end portion of the strut-like part 48 there may be provided a plate or pad-like element '92 which may be formed of any suitable material and, if desired, such material may be resil ient in nature or possess other desirable properties with the element 92 being disposed to engage the A-fr-ame support structure 50 when the boom structure 112 is raised to the vertical in order to reduce noise, shock and wear of the boom stop apparatus 24.

The sleeve-like part 44 of the first link-like member 28 carries a friction brake assembly 94, note FIGURES 2, 4 and 5 of the drawing, for impeding, retarding or otherwise controlling the telescoping of the part 38 relative thereto in order to assure that the second link-like member 34 is pivotally moved into supporting engagement with the A-frame support structure 50 prior to retraction or contraction of the first link-like member 28 and thus prior to the compression of air in the container or cylinder 46. This controlled sequential operation of the linkage device 26 of the boom stop apparatus 24 is important since the second link-like member 34- is allowed by the guide 54 to move through more than 90 from a first position, as shown by solid lines in FIGURES '1 and 2 of the drawing, whereat the boom structure 12 is in a lower or substantially horizontal position, to a second position, as illustrated by dotted lines in FIGURES l and 2 of the drawing, whereat the boom structure '12 is being cushioned, limited, hindered, stopped, arrested, restrained or otherwise prevented from moving further backward or recoiling, as explained above, with the second link-like member 3 4 being supported through the plate or padlike element 92 by the inclined part 96 of the A-frarne support structure 50. This initial controlled sequential movement of the first 28 and the second 34 link-like members permits the telescoping parts 38 and 44 of the first link-like member 28 to be relatively shorter than if such movement was not so controlled and at the same time still enables and allows the boom structure 12 to be lowered to ground level. The second link-like member 34 is first moved back into engagement with the inclined part 96 of the A-frame support structure 50 before the parts 33 and 44 of the first link-like member 28 begin to telescope or the boom structure 12, while being raised to a vertical, would bring the longitudinally extending axes of the parts 38 and 44 beyond a coplanar relationship with the longitudinal axis of second member 34. If the parts 38 and 44 were so brought to this position without prior rearward movement of the second link-like member 34, the linkage device 26 might jack-knife with the second link-like member 34 being forced forwardly and the forces placed on the guide 54 instead of on the inclined part 96 of the A-frame support structure 50. Under these conditions, the guide 54 will break allowing the second link-like member 34 to engage the inclined part 96 of the A-frame structure 50 at a location intermediate the pivot thereof and the boom structure pivot 14. In this conditioned position, the boom stop apparatus '24 is not eifective to cushion, limit, hinder, stop, arrest, restrain or otherwise prevent the recoil or movement of the boom structure 12, as desired.

The friction brake assembly 94 is provided with a plate 98, note FIGURES 2 and 5 of the drawing, carrying a brake shoe 1% that extends through an opening 192 in the part 44 to frictionally engage the part 38. The brake assembly 94- is mounted on the part 44 by two threaded pins 164 that project from the part 44 and receive tighteners and adjustments 106. The pin-s 194 are received through two bores in the plate 98 and resilient elements 108 are interposed between the tighteners and adjustments 166 and the plate 98 on the pins 104. The tighteners and adjustments 106 are shown as being of not form and may be tightened or loosened to adjust the effective drag of the brake assembly 94, as required.

In FIGURE 2 of the drawing, it is to be noted that further adjustment is provided for the boom stop appa ratu-s 24 which is in the form of a bracket 110 which is adjustably movable and securably supported and carried by the inclined part 96 of the A-frame support structure 50 and to which the second link-like member 34 is pivotally secured.

In operation, as the boom structure 12 is being raised, the brake assembly 98 impedes telescoping of the part 38 relative to the part 44 and thereby the part 48 is forced back upon the part 96 of the A-frarne support structure 50. When the plate or pad-like element 92 engages the inclined part 96 of the support structure 50 the part 38 of the first link-like member 28 begins to telescope relative to the part 44 by overcoming the frictional drag of the brake assembly 94. During this telescoping, stop-guide rod-like part 60 is received into the confines of the part 40. As the boom structure 12 is further raised, this telescoping relationship of parts 38 and 44 continues until the abutment 56 of the part 38 engages the clevis type connection 70 located between the guide-stop rod-like part 60 and the piston rod 66. Since the clevis type connection 70 is positively engaged with the piston 64 of the air cylinder 46 through the piston rod 66, any further upward movement of the boom structure 12 will cause air in the air cylinder 46 to be further compressed. The air cylinder 46 is pre-cha-rged to approximately 100 psi. through the conduit structure 84, the check valving 88 and the intake port 82. This air supply system only makes up for leakage that escapes the air cylinder 46 past the piston 64 through the exhaust port 86 to atmosphere.

By reason of the adjustments 72 and it is possible to begin compressing air in the air cylinder 46 at any position of the boom stmcture 12 prior to the boom structure 12 reaching a vertical position and thereby effect operation of the boom stop apparatus 24 at a predetermined desired boom angle relative to a horizontal, as desired by the operator.

While the invention has been shown, illustrated, de scribed and disclosed in terms of an embodiment or modification which it has assumed in practice, the scope of the invention should not be deemed to be limited by the precise embodiment or modification as herein shown, illustrated, described and disclosed, and other embodiments or modifications are intended to be reserved as they fall within the scope of the claims here appended.

We claim as our invention:

1. In combination with a crane assembly having an elongate boom structure pivotally supported by an upper works,

apparatus for restraining movement of the boom structure toward a vertical, said apparatus comprising an elongate longitudinally extendible and retractable first member having one part thereof pivotally connected to the boom structure at a location thereon which is intermediate the end portions thereof and another part telescopically supporting the one part for generally longitudinal movement relative thereto,

a source of air under pressure carried by the another part of said first member,

a stop-guide-abutment arrangement for enabling the one part of said first member to further compress such air in response of the first member on movement of the boom structure toward a vertical,

a second elongate member pivotally connected to the another part of the first member and to the upper works of the crane assembly,

said second member being movable between a first position whereat the first member is extended and a seciond position whereat the first member is retracted with the second member being in engagement with an inclined part of the upper works of the crane assembly, and

structure for retarding the retraction of the first member on movement of the boom structure toward a vertical until after the second member has been urged to the second position thereof.

2. The combination as set forth in claim 1 wherein said source of air under pressure comprises 3. In combination with a crane assembly having an upper works and elongate boom structure pivotally mounted to the upper works,

apparatus for cushioning the boom structure against movement thereof toward a vertical, said apparatus comprising a linkage device having at least two elongate members which are pivotally connected together with one of the members being further pivotally connected to the boom structure and the other member being further pivotally connected to the upper works of the crane assembly,

said one member of the linkage device having telescopically disposed longitudinally extendable and retractable parts,

a. source of air under pressure carried by one of the parts of said one member,

said source of air being compressible on retraction of said one member of the linkage device on movement of the boom structure toward a vertical, and

structure for restraining the retraction of the one member until the other member of the linkage device is in engagement with the upper works of the crane assembly.

4. In combination with a crane assembly having an upper works and elongate boom structure pivotally mounted to the upper works,

apparatus for cushioning the boom structure against movement thereof toward a vertical, said apparatus comprising a linkage device having at least two elongate members,

one of said member having telescopically disposed longitudinally extendible and retractable parts,

one of the parts of said one member being pivotally connected to the boom structure with the other part thereof being pivotally connected to the other memher,

said other member being further pivotally connected to the upper Works of the crane assembly,

a source of fluid under pressure carried by the other 7 part of said one member,

an arrangement for enabling the one part of said one member on retraction thereof to compress such fluid on movement of the boom structure toward a vertical, and

structure for restraining the retraction of the one member until after the other member of the linkage device engages a part of the upper works.

5. The combination as set forth in claim 4 together with structure for adjusting the members of the linkage device to vary the effect thereof.

6. In combination with load-handling equipment having elongate boom structure pivotally supported by base support structure,

apparatus for restraining movement of the boom structure toward a vertical, said apparatus comprising an elongate extendible and retractable first member having one part thereof pivotally connected to the boom structure and a second part telescopically supporting the first part for generally longitudinal movement relative thereto,

a source of air under pressure carried by the first member,

a stop-guide-abutment arrangement for enabling the part of the first member on retraction thereof in response to movement of the boom structure toward a vertical to further compress such air,

a second elongate member pivotally connected to the second part of the first member and to the base sup port structure,

said second member being movable between a first position whereat the first member is extended and a second position whereat the first member is retracted with the second member being in engagement with the base support structure when disposed in the second position, and

structure for retarding the retraction of the first men ber on movement of the boom structure toward a ivertical until the second member has been urged to the second position thereof.

7. In combination with load-handling equipment having base support structure and elongate boom structure pivotally mounted to the base support structure,

apparatus for restraining the boom structure against movement toward a vertical, said apparatus comprising a linkage device having at least two elongate members,

one of said members having telescopically disposed longitudinally extendible and retractable parts,

one of the parts of said one member being pivotally connected to the boom structure of the equipment with the other part thereof being pivotally connected to the other member,

said other member being further pivotally connected to the base support structure of the equipment, and

structure for restraining the retraction of the one member of the linkage device on movement of the boom structure toward a vertical until the other member is in engagement with the base support structure of the equipment.

8. Apparatus for restraining movement of boom structure which is pivotally mounted to base support structure on movement thereof toward a vertical, said apparatus comprising an elongate extendible and retractable first member pivotally connected to the boom structure,

a source of air under pressure carried by the first member,

an arrangement for enabling said first member on retraction thereof in response to movement of the boom structure toward a vertical to further compress such (arr,

a second elongate member pivotally mounted to the first member and to the base support structure,

said second member being movable between a first position whereat the first member is extended and a second position whereat the first member is retracted with the second member being in engagement with the base support structure when disposed in the second position, and

structure for retarding the retraction of the first member on movement of the boom structure toward a vertical until the second member has been urged to the second position thereof.

9. Apparatus for limiting movement of boom structure which is pivotally mounted to base support structure on movement thereof toward a vertical, said apparatus comprising an elongate extendible and retractable first member having one part pivotally connected to the boom structure and another part telescopically supporting the one part for generally longitudinal movement relative thereto,

a source of fluid under pressure carried by the another part of the first member,

an arrangement for enabling said one part of the first member on retraction thereof in response to movement of the boom structure toward a vertical to further compress such fluid,

a second elongate member pivotally connected to the another part of the first member and to the base support structure,

said second member being movable between a first position whereat the first member is extended and a second position whereat the first member is retracted with the second member being in engagement with the base support structure when disposed in the second position, and

structure for retarding the retraction of the first member on movement of the boom structure toward a vertical until the second member has been urged to the second position thereof.

10. The apparatus as set forth in claim 9 wherein said source of fluid under pressure comprises a cylinder and piston assembly wherein said piston has a rod extending beyond the confines of the cylinder, and

said arrangement comprises an elongate rod-like part extending between the piston rod and the one part of the first member together with an abutment in the one part of the first member for engaging the piston rod on retraction of the first member.

11. Apparatus for resraining movement of boom structure which is pivotally mounted to base support structure -on movement thereof toward a vertical, said apparatus comprising a linkage device having a plurality of elongate members one of which is extendible and retractable,

said one member being pivotally connected to the boom structure and having a source of fluid under pressure supported thereon,

an arrangement for enabling said one member on retraction thereof in response to movement of the boom structure toward a vertical to further compress such fluid,

a second elongate member pivotally connected to the one member and to the base support structure,

said second member being movable between a first position whereat the one member is extended and a second position whereat the one member is retracted with the second member being in engagement with the base support structure when disposed in the second position, and

structure for adjusting the relative positions and effects of the members of the linkage device.

'12. Apparatus for limiting movement of boom structure which is pivotally mounted to base support structure on movement thereof toward a vertical, said apparatus comprising an elongate extendible and retractable first member having a plurality of telescopically disposed parts one of which is pivotally connected to the boom structure,

a second elongate member pivotally connected to another one of the parts of the first member and to the base support structure,

said second member being movable between a first position whereat the first member is extended and a second position whereat the first member is retracted with the second member being in engagement with the base support structure when disposed in the second position, and

structure for restraining the retraction of the first member on movement of the boom structure toward a vertical until after the second member of the apparatus has been urged to the second position thereof.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN COMBINATION WITH A CRANE ASSEMBLY HAVING AN ELONGATE BOOM STRUCTURE PIVOTALLY SUPPORTED BY AN UPPER WORKS, APPARATUS FOR RESTRAINING MOVEMENT OF THE BOOM STRUCTURE TOWARD A VERTICAL, SAID APPARATUS COMPRISING AN ELONGATE LONGITUDINALLY EXTENDIBLE AND RETRACTABLE FIRST MEMBER HAVING ONE PART THEREOF PIVOTALLY CONNECTED TO THE BOOM STRUCTURE AT A LOCATION THEREON WHICH IS INTERMEDIATE THE END PORTIONS THEREOF AND ANOTHER PART TELESCOPICALLY SUPPORTING THE ONE PART FOR GENERALLY LONGITUDINAL MOVEMENT RELATIVE THERETO, A SOURCE OF AIR UNDER PRESSURE CARRIED BY THE ANOTHER PART OF SAID FIRST MEMBER, A STOP-GUIDE-ABUTMENT ARRANGEMENT FOR ENABLING THE ONE PART OF SAID FIRST MEMBER TO FURTHER COMPRESS SUCH AIR IN RESPONSE OF THE FIRST MEMBER ON MOVEMENT OF THE BOOM STRUCTURE TOWARD A VERTICAL, A SECOND ELONGATE MEMBER PIVOTALLY CONNECTED TO THE ANOTHER PART OF THE FIRST MEMBER AND TO THE UPPER WORKS OF THE CRANE ASSEMBLY, SAID SECOND MEMBER BEING MOVABLE BETWEEN A FIRST POSITION WHEREAT THE FIRST MEMBER IS EXTENDED AND A SECOND POSITION WHEREAT THE FIRST MEMBER IS RETRACTED WITH THE SECOND MEMBER BEING IN ENGAGEMENT WITH AN INCLINED PART OF THE UPPER WORKS OF THE CRANE ASSEMBLY, AND STRUCTURE FOR RETARDING THE RETRACTION OF THE FIRST MEMBER ON MOVEMENT OF THE BOOM STRUCTURE TOWARD A VERTICAL UNTIL AFTER THE SECOND MEMBER HAS BEEN URGED TO THE SECOND POSITION THEREOF. 